Adaptive intelligent circulation control methods and systems

ABSTRACT

Adaptive intelligent circulation control methods and systems are used to help increase the comfort and/or reduce energy usage and equipment wear. In one illustrative embodiment, the circulation and/or ventilation time is adjusted based on one or more environmental conditions inside or outside the building structure. In another illustrative embodiment, the circulation and/or ventilation time may be adjusted based on the current time of day, current time of year, and/or the current schedule period. In another illustrative embodiment, the circulation and/or ventilation time is randomized over time. The start time, end time, and/or length of a circulation and/or ventilation cycle may be randomly set.

This application is a continuation of U.S. patent application Ser. No.11/674,805, filed Feb. 14, 2007, which is a continuation of U.S. patentapplication Ser. No. 10/753,589, filed Jan. 7, 2004, which areincorporated herein by reference.

FIELD

The present invention is related to the field of heating, ventilation,and air conditioning (HVAC) systems. More particularly, the presentinvention is related to control methods for HVAC systems.

BACKGROUND

HVAC systems are commonly used to control various environmentalconditions within building structures including, for example,temperature, humidity, ventilation, etc. In doing so, a fan or the likeis often used to force air through the HVAC system and provideconditioned air to the inside space of the building structure. Whendoing so, the air is circulated within the structure. Air circulationcan help increase the comfort inside the building structure by, forexample, equalizing the temperature, humidity and other environmentalconditions within the structure.

Some HVAC systems have one or more circulation modes. For example, someHVAC systems include a fan “on” mode, where the fan is “on”continuously, regardless of whether the HVAC system is called tocondition the air in the building structure. A “circulate” fan mode isalso sometimes provided, which typically runs the fan for a fixed periodof time during each hour, such as 20 minutes each hour. These and othercirculation modes may help circulate the air within a buildingstructure.

In some HVAC systems, fresh air ventilation is also provided. Fresh airventilation has become increasingly popular, especially because newbuilding structures have become more energy efficient and consequentlymore air tight. Fresh air ventilation is typically used to replace staleair inside the building structure with fresh outside air. Fresh airventilation often uses the fan of the HVAC system, and thus alsoprovides air circulation within the building structure. Heat exchangersare sometimes used to exchange heat between the outgoing stale air andthe incoming fresh outside air to help reduce the energy costsassociated with heating or cooling building structure.

While circulation and/or ventilation are often desirable,over-circulation and/or over-ventilation can result in increased energycosts and excessive equipment wear. What would be desirable, therefore,are adaptive circulation and/or ventilation control methods and systemsthat provide desired circulation and/or ventilation levels, whileminimizing energy costs and equipment wear.

SUMMARY

The present invention relates to adaptive circulation and/or ventilationcontrol methods and systems for providing controlled circulation and/orventilation levels in a building structure. In one illustrativeembodiment, the circulation and/or ventilation time is adjusted based onone or more environmental conditions inside or outside the buildingstructure. For example, the HVAC system may include one or more sensorsfor sensing one or more environmental conditions in and/or around thebuilding structure. The one or more sensors may include, for example,one or more temperature sensors, humidity sensors, air quality sensors,gas sensors, or any other suitable sensors, as desired. HVAC systemsettings such as set point values, system mode (e.g. heat, cool or off),whether the building is expected to be occupied or unoccupied, time ofday, time of year, etc. may also be used in some embodiments. Based onthe output(s) of the sensors, and in some cases the system settings, theHVAC system may adjust the circulation and/or ventilation timeaccordingly.

In another illustrative embodiment, the circulation and/or ventilationtime may be randomized over time. For example, in some illustrativeembodiments, the start time, the end time, and/or the length of thecirculation and/or ventilation cycle may be randomly set. This mayprovide a number of advantages including, for example, increasedcomfort, reduced power spiking in HVAC systems that have multipleequipment installations, etc.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram of an illustrative HVAC system;

FIGS. 2A-2C show illustrative user interfaces for the controller of theHVAC system of FIG. 1;

FIG. 3 shows a flow chart of one illustrative method in accordance withthe present invention;

FIG. 4 shows a flow chart of another illustrative method in accordancewith the present invention;

FIG. 5 shows a flow chart of another illustrative method in accordancewith the present invention;

FIG. 6 is a flow chart of an illustrative method for randomizing thestart time of a fan “on” cycle of an HVAC system in accordance with thepresent invention;

FIG. 7 is a flow chart of an illustrative method for randomizing thelength of a fan “on” cycle of an HVAC system in accordance with thepresent invention;

FIG. 8 is a timing diagram showing a number of illustrative fan cyclesin accordance with the present invention; and

FIGS. 9A-9B show a flow chart in block form of another illustrativemethod in accordance with the present invention.

DETAILED DESCRIPTION

The following detailed description should be read with reference to thedrawings. The drawings, which are not necessarily to scale, depictillustrative embodiments and are not intended to limit the scope of theinvention.

FIG. 1 is a schematic diagram of an illustrative HVAC system. Theillustrative HVAC system is used for controlling one or moreenvironmental conditions of an inside space of a structure 20. Theillustrative HVAC system includes a heating apparatus 12, a coolingapparatus 14, a heat exchanger 16, and a circulation/ventilation fan 18.The HVAC system creates air circulation in the structure 20 using thefan 18 and ductwork. Also shown is a controller 22 that receivesenvironmental information and user inputs from a thermostat 24, whichmay also include a humidistat. Additional sensors may be placed in andaround the structure 20 for sensing both internal and externalconditions.

As an optional feature, and for some HVAC systems, a fresh air vent 26and damper 28 may be included to enable fresh air ventilation into thestructure 20. The fresh air vent 26 and damper 28 allow constant,selective or intermittent infusion of fresh air from outside thestructure 20, as desired. While the methods and systems of the presentinvention may be used for HVAC systems that include fresh airventilation, it is not required in all embodiments.

Typically, a user will input information such as a set point temperatureand/or a schedule of set point temperatures, humidity levels,circulation rates, etc, into the controller 22. The controller 22 mayreceive information through any suitable device, such as the controllershown in FIGS. 2A-2C. Occupancy may also be monitored by the controller22 either by the use of sensors such as motion sensors, by receivinguser-input occupancy information, by derivation from a controllerschedule, or through any other suitable mechanism. For systemsincorporating fresh air ventilation, inputs regarding desired fresh airventilation levels may also be provided to the controller 22 in anysuitable manner. The controller 22 may periodically call for heating,cooling, humidity control, circulation, and/or fresh air ventilation,and activate the appropriate components 12, 14, 18, 28.

FIGS. 2A-2C show illustrative user interfaces for the controller of theHVAC system of FIG. 1. The user interfaces shown in FIGS. 2A-2C includea touchpad having “touchkey” areas where a user can make selectionsusing virtual or soft “buttons”. The user interfaces shown in FIGS.2A-2C are only illustrative, and other controllers with other displaysand/or selection mechanisms may be used, if desired.

FIG. 2A shows a first user interface 50 which includes a day indicator52, an inside temperature indicator 54, a set point indicator 56, and anoutside temperature indicator 58. The temperature indicators 54 and 58relay information gathered by inside and outside temperature sensors,respectively. The day indicator 52 indicates the current day of theweek, typically based on an internal or external clock, which also mayenable a daily or weekly schedule. The controller status is shown at 60,where it is indicated that a preprogrammed schedule is currently beingfollowed. The user interface 50 also indicates the current time of day62.

The lower portion of the user interface 50 includes several virtual orsoft “buttons” generally shown at 64. In the illustrative user interface50, the virtual or soft “buttons” 64 can be used to change the mode ofthe controller (the controller is shown having schedule and hold modes),to access clock information, to change screen options, and/or to accessfurther options. The user interface 50 also includes a fan statusindicator, which may include a virtual or soft “button” 66. When thevirtual or soft “button” 66 is depressed, and as further described belowwith respect to FIG. 2B, the user may select a particular fan mode. Inthe illustrative embodiment, the available fan modes include, forexample, a fan “on” mode, a fan “auto” mode and a fan “circulate” mode.

The illustrative user interface 50 of FIG. 2A may further include asystem mode indicator 68, which includes a virtual or soft “button” 68for changing the system mode. In FIG. 2A, the system mode is set toheat, as shown at 68. However, other modes may include, for example, acool mode, an auto mode, and an off. Other modes may also be provided,as desired.

FIG. 2B shows an illustrative user interface 70 which may be displayedafter the virtual or soft “button” 66 of the fan status indicator ofFIG. 2A has been depressed. The illustrative user interface 70 displaysa fan mode selector 74, which allows the user to select a desired fanmode. As described above, the available fan modes may include, forexample, a fan “on” mode, a fan “auto” mode and a fan “circulate” mode.In the fan “on” mode, the fan of the HVAC system may be “on”continuously, regardless of whether the HVAC system is making a call(e.g. heat, cool) to condition the air in the building structure. In the“auto” mode, the fan may run during the HVAC system calls that arenecessary to meet the desired HVAC schedule. In the “circulate” mode,the fan may run according to the adaptive circulation and/or ventilationcontrol methods, as further described herein. In some embodiments, theadaptive circulation and/or ventilation control methods of the presentinvention may be included in the fan “auto” mode, if desired. It shouldbe recognized that these fan “modes” are only illustrative, and they arenot intended to limit the scope of the present invention.

In some embodiments, a circulation duty cycle (CDC) indicator 72 mayalso be provided to allow the user to enter a desired circulation dutycycle index, which may correspond to the amount of circulation desiredby the user. In the illustrative embodiment, the index is set to “30”. Avalue of “30” may correspond to, for example, an initial or startingvalue for the circulation duty cycle of 30 percent. As further describedbelow, the initial or starting value for the circulation duty cycle maybe changed by the adaptive circulation and/or ventilation controlmethods of the present invention. In the illustrative embodiment, the uparrow 78 and the down arrow 79 may be used to increase or decrease,respectively, the desired circulation duty cycle index. As generallyshown at 76, the user interface 70 may also include virtual or soft“buttons” labeled “DONE” and “CANCEL”, which may allow the user to exitthe user interface 70 and return to the user interface 50 shown in FIG.2A.

In another embodiment, rather than having the user enter an index thatcorresponds to, for example, a particular percentage, other manners ofdata input may be chosen. For example, the user may, for example, have adial or other scale having positions from one to ten, where the user canselect a level within the range defined by the scale. Higher numbers mayindicate a higher circulation level, while lower numbers may indicate alower circulation level. Alternatively, the user may be provided with anoption to select, for example, LESS, NORMAL, or MORE circulation. In yetanother embodiment, with the system operating the user may modifyoperation by selecting to have MORE or LESS circulation than that whichis already occurring. That is, the user may be provided with options ofMORE or LESS, relative to the then existing circulation conditions.

FIG. 2C illustrates another user interface 80, which may be displayedwhen the “SCHED” button 81 of FIG. 2A is depressed. The user interface80 includes day indicators 82, a heating set point indicator 84, acooling set point indicator 86, a time indicator 88, a fan modeselector/indicator 90, period selectors/indicators 92, and edit controlkeys 94. The user interface 80 may be used to edit the schedule of thecontroller 22 (see FIG. 1). In the illustrative embodiment, each dayincludes four periods including a “wake” period, a “leave” period, a“return” period and a “sleep” period. These periods are onlyillustrative. Each period may be assigned a different set point, and inthe illustrative embodiment, a different fan mode, if desired. In FIG.2C, the heat set point 84, the cool set point 86, the fan mode 90, aswell as the beginning time 88, are displayed for the “leave” period ofthe Wednesday schedule. With such a schedule, the controller 22 (seeFIG. 1) may expect the building structure to be unoccupied during the“Leave” period, and occupied during the other periods.

FIG. 3 shows a flow chart of one illustrative method in accordance withthe present invention. The flow chart is entered at start block 300.Control is then passed to block 302. Block 302 reads a value of one ormore sensors to determine at least one environmental condition in and/oraround a building. The one or more sensors may include, for example, oneor more temperature sensors, humidity sensors, air quality sensors, gassensors, or any other suitable sensors, as desired. The environmentalconditions may include, for example, inside temperature, outsidetemperature, inside humidity, outside humidity, inside air quality,outside air quality, occupancy of the inside space, or any other desiredenvironmental condition as desired. It is contemplated that the sensorsused to detect the one or more environmental conditions may be wired orwireless device. In some embodiments, for example, the sensors mayprovide sensor data via a communications system such as a phone lineand/or the Internet. For example, air quality data may be collected byone or more sensors at an airport or the like, and the sensor data maybe retrieved across a phone line or the internet, if desired. Also, forsensors within the building structure, the sensors may provide sensordata to a controller via one or more wires, a bus, or via a wireless(e.g. RF) connection.

In some embodiments, some HVAC system settings may also be read, such asset point values, system mode (e.g. heat, cool or off), whether thebuilding is expected to be occupied or unoccupied, time of day, time ofyear, etc. Control is then passed to block 304. Block 304 changes thefan circulation amount or level based on at least one of theenvironmental conditions sensed in block 302, and in some cases, on oneor more of the HVAC system settings.

In one illustrative example, when the outside temperature is warm, thefan circulation amount (in some cases including ventilation) may beincreased to increase the cooling effect often felt by occupants causedby moving air, and/or to help de-stratify the air to get a more eventemperature distribution in the inside space. In another illustrativeexample, when the inside humidity is low, the fan circulation amount (insome cases including ventilation) may be increased to provide more airthrough a humidifier of the HVAC system. In another illustrativeexample, when the HVAC system is in a heating mode, and the set point islow, the fan circulation amount (in some cases including ventilation)may be reduced to help reduce the cooling effect often felt by occupantscaused by moving air. In yet another example, when the HVAC system is ina cooling mode, and the set point is high, the fan circulation amount(in some cases including ventilation) may be increased to increase thecooling effect often felt by occupants caused by moving air.

In yet another example, when the HVAC system is in a heating mode, andthe outside temperature is closer to the set point temperature thusreducing the load on the HVAC system, the fan circulation amount (insome cases including ventilation) may be increased to increase thenumber of times that the air passes through the air cleaner of the HVACsystem. This may be desirable because when the outside air temperatureis closer to the set point temperature, the amount of time that the HVACsystem will be run to satisfy the heat load may be less. Likewise, whenin a heating mode and the inside temperature is more than the set point,the HVAC system will run less, and the fan circulation amount (in somecases including ventilation) may be increased to increase the number oftimes that the air passes through the air cleaner of the HVAC systemand/or to help de-stratify the air to get a more even temperaturedistribution in the inside space.

Also, when in a cooling mode, and the inside temperature is less thanthe set point, the HVAC system will tend to run less and the fancirculation amount (in some cases including ventilation) may beincreased to increase the number of times that the air passes throughthe air cleaner of the HVAC system and/or to help de-stratify the air toget a more even temperature distribution in the inside space.

In yet another example, when in a heating mode, and when the outdoorhumidity is relatively low, the fan circulation amount (includingventilation) may be reduced to help reduce the amount of dry air that isbrought inside. Likewise, when in a cooling mode, and when the outdoorhumidity is relatively high, the fan circulation amount (includingventilation) may be reduced to help reduce the amount of humid air thatis brought inside.

In yet another example, if the indoor air quality is poor, the fancirculation amount (including ventilation) may be increased to increasethe number of times that the air passes through the air cleaner of theHVAC system. Likewise, if the outdoor air quality is poor, the fancirculation amount (with ventilation) may be decreased to decrease theamount of outside air that is brought into the inside space, orincreased (without ventilation) to increase the amount of air thatpasses through the HVAC filter.

These are just a few examples of adaptively controlling the circulationand/or ventilation time based on one or more environmental conditions inand/or around the building structure, and in some cases, one or moresystem settings of the HVAC system. Once the desired circulation levelhas been changed by block 304, the illustrative method may be exited, asshown at 306. In some cases, the method may be repeated constantly orperiodically to control the circulation level within a buildingstructure.

FIG. 4 shows a flow chart of another illustrative method in accordancewith the present invention. The flow chart is entered at start block400. Control is then passed to block 402. Block 402 determines whatschedule period the HVAC system is currently operating in. For example,and as shown in FIG. 2C above, the HVAC system may be operating in the“Leave” time period on Wednesday. Alternatively, or in addition, theschedule time period may correspond to a season, such as fall, winter,spring or summer. Once the current schedule period has been identified,control is then passed to step 404. Step 404 changes the desiredcirculation level based on the schedule period that the HVAC system iscurrently operating. For example, during the warmer afternoons of asummer day, the fan circulation amount (in some cases includingventilation) may be increased to increase the cooling effect often feltby occupants caused by moving air. Likewise, during the cooler nights ofa winter day, the fan circulation amount (in some cases includingventilation) may be decreased to help reduce the cooling effect oftenfelt by occupants caused by moving air.

In some cases, the schedule of the HVAC system controller may be used todetermine if the building is expected to be occupied or unoccupied. Forexample, during a “Leave” period of a typical HVAC system schedule, thecontroller may determine that the inside space is expected to beunoccupied. During unoccupied periods, the fan circulation amount (insome cases including ventilation) may be reduced to save energy and/orreduce equipment wear.

These are just a few examples of adaptively controlling the circulationand/or ventilation time based on one or more schedule periods, and insome cases, one or more system settings of the HVAC system. Once thedesired circulation level has been changed by block 404, theillustrative method may be exited, as shown at 406. In some cases, themethod may be repeated constantly or periodically to control thecirculation level within a building structure. It is contemplated thatthe illustrative method of FIG. 4 may be combined with the method ofFIG. 3, if desired.

FIG. 5 shows a flow chart of another illustrative method in accordancewith the present invention. The flow chart is entered at start block500. Control is then passed to block 502. Block 502 determines a presenttime of year. For example, the present time of year may correspond to aseason, such as fall, winter, spring or summer, a month or any othertime of year, as desired. Once the present time of year has beenidentified, control is passed to step 504. Step 504 changes the desiredcirculation level based on the present time of year. For example, duringthe warmer summer season, the fan circulation amount (in some casesincluding ventilation) may be increased to increase the cooling effectoften felt by occupants caused by moving air. Likewise, during thecooler winter season, the fan circulation amount (in some casesincluding ventilation) may be decreased to help reduce the coolingeffect often felt by occupants caused by moving air.

These are just a few examples of adaptively controlling the circulationand/or ventilation time based on the present time of year, and in somecases, one or more system settings of the HVAC system. Once the desiredcirculation level has been changed by block 504, the illustrative methodmay be exited, as shown at 506. In some cases, the method may berepeated constantly or periodically to control the circulation levelwithin a building structure. It is contemplated that the illustrativemethod of FIG. 5 may be combined with the methods of FIG. 3 and FIG. 4,if desired.

In another illustrative embodiment, the circulation (sometimes includingventilation) time may be randomized over time. For example, in someillustrative embodiments, the start time, the end time, and/or thelength of the fan cycle (sometimes including ventilation) may berandomly set. This may provide a number of advantages including, forexample, increased comfort, reduced power spiking in HVAC systems thathave multiple equipment installations, etc.

FIG. 6 is a flow chart of an illustrative method for randomizing thestart time of a fan “on” cycle of an HVAC system in accordance with thepresent invention. The fan “on” cycle may be a circulation cycle, aheating cycle, a cooling cycle, or any other cycle where there has a fan“on” time and a fan “off” time. The flow chart is entered at start block600. Control is then passed to block 602. Block 602 provides a random orpseudo random start time delay. The random or pseudo random start timedelay may be generated by a random number generator. Alternatively, orin addition, the random or pseudo random start time delay may beselected from an ordered list of start time delays that very from one tothe next, or by any other suitable method for generating an apparentrandom or pseudo random start time delay, as desired. Control is thenpasses to block 604. Block 604 delays at least one of the fan “on” timeperiods by an amount that is at least related to the random or pseudorandom start time delay. The illustrative method may then be exited, asshown at 606. In some cases, the method shown in FIG. 6 may be repeatedconstantly or periodically to help randomize the fan “on” start times.In addition, the illustrative method of FIG. 6 may be combined with themethods of FIGS. 3-5, if desired.

FIG. 7 is a flow chart of an illustrative method for randomizing thelength of a fan “on” cycle of an HVAC system in accordance with thepresent invention. The flow chart is entered at start block 700. Controlis then passed to block 702. Block 702 provides a random or pseudorandom time period. The random or pseudo random time period may begenerated by a random number generator. Alternatively, or in addition,the random or pseudo random time period may be selected from an orderedlist of time periods that very from one to the next, or by any othersuitable method for generating an apparent random or pseudo random timeperiod, as desired. Control is then passes to block 704. Block 704modifies the length of at least one fan “on” time period by an amountthat is at least related to the random or pseudo random time period,resulting in a new fan “on” time period length. Control is then passedto block 706. Block 706 operates the fan using the new fan “on” timeperiod length. The illustrative method may then be exited, as shown at708. In some cases, the method shown in FIG. 7 may be repeatedconstantly or periodically to help randomize the fan “on” time lengths.It is contemplated that the illustrative method of FIG. 7 may becombined with the methods of FIGS. 3-6, if desired.

FIG. 8 is a timing diagram showing a number of illustrative fan cyclesin accordance with the present invention. A first line 800 illustratesstandard fan cycles N and N+1. Fan cycle N begins at times A, and Fancycle N+1 begins at time B. The fan cycle has a first fan “on” time 802a beginning at time A, followed by a first fan “off” time 804 a,followed by a second fan “on” time 802 b beginning at time B, followedby a second fan “off” time 804 b. The first fan “on” time 802 a and thesecond fan “on” time 802 b both begin at the beginning of theirrespective fan cycles N and N+1, respectively, and have the same length.

A second line 806 shows a fan cycle that includes a randomized starttime delay for each cycle N and N+1. The second line 806 shows a fancycle that has a first fan “on” time 808 a, followed by a first fan“off” time 810 a, followed by a second fan “on” time 808 b, followed bya second fan “off” time 810 b. The start time of the first fan “on” time808 a is delayed from time A by a first random or pseudo random starttime delay, and the start time of the second fan “on” time 808 b isdelayed from time B by a second random or pseudo random start timedelay. For the second line 806, the length of the first fan “on” time808 a and the length of the second fan “on” time 808 b are the same. Athird line 812 shows that the random or pseudo random start time delaysmay be positive or negative, as desired.

A fourth line 816 shows a fan cycle that includes a randomized fan “on”time length for each cycle N and N+1. The fourth line 816 shows a fancycle that has a first fan “on” time 818 a beginning at time A, followedby a first fan “off” time 820 a, followed by a second fan “on” time 818b beginning at time B, followed by a second fan “off” time 820 b. Thereis no start time delay for the first fan “on” time 818 a or the secondfan “on” time 818 b. However, the length of the first fan “on” time 818a and the second fan “on” time 818 b have been randomly selected. Thus,in the illustrative embodiment, the length of the first fan “on” time818 a is longer than the length of the second fan “on” time 818 b.

A fifth line 828 shows a fan cycle that includes a randomized start timedelay and a randomized fan “on” time length for each cycle N and N+1.The fifth line 828 shows a fan cycle that has a first fan “on” time 830a, followed by a first fan “off” time 832 a, followed by a second fan“on” time 830 b, followed by a second fan “off” time 832 b. The starttime of the first fan “on” time 830 a is delayed from time A by a firstrandom or pseudo random start time delay, and the start time of thesecond fan “on” time 830 b is delayed from time B by a second random orpseudo random start time delay. In addition, the length of the first fan“on” time 830 a and the length of the second fan “on” time 830 b arerandomly selected or changed, and thus are shown having differentlengths.

FIGS. 9A-9B show a flow chart in block form of another illustrativemethod in accordance with the present invention. From a start block 900,the method begins by setting a circulation duty cycle to a defaultvalue, as shown at 902. The circulation duty cycle may be a desiredcirculation duty cycle percentage or level. This may represent theamount or percentage of time during which the circulation fan of an HVACsystem (typically a fan connected to ductwork) is on during a given timeperiod. For purposes of simplicity, the present disclosure is presentedin terms of hours, however this is not required in all embodiments. Thecirculation duty cycle can be a measure of time for a given time block,or it may be a percentage. For example, if the circulation duty cycle isfifty percent, the circulation (sometimes including ventilation) of anHVAC system may be turned on for thirty minutes in an hour. The defaultvalue may be provided to the HVAC controller via its factory settings,may be set by a technician during installation, or may be set by a user.

Next, and in the illustrative embodiment, the circulation duty cycle maybe adjusted based on the current set point temperature, as shown at 904.The set point temperature may be an input provided by the user. For someHVAC controllers, a user is allowed to provide a schedule, wherein theset point may vary throughout a day and/or week. This may be relevant tothe circulation duty cycle in that the desired circulation duty cyclecan vary depending upon the set point temperature. For example, when thesystem is in a heating mode, and the set point is low, the equipment mayoperate less because the heating load is light. The ventilationcirculation duty cycle may be reduced to avoid creating a cooling effectthat may be felt by occupants caused by the movement of air.Alternatively, or in addition, when in a cooling mode, more aircirculation may create a cooling effect, so the circulation duty cyclemay be increased to improve the cooling effect caused by air movement.It should be noted that block 904 may be a return point for the method,since the illustrative method may loop back from FIG. 9B to theadjustment for set point temperature 904, as shown.

The illustrative method then may adjust the circulation duty cycle basedon indoor humidity, as shown at block 906. For example, some systemsinclude a humidifier that operates whenever the fan is “on”. Thus, whenin a heating mode and with a low indoor humidity level, the circulationduty cycle may be increased to encourage higher humidity by creatingmore air movement through the humidifier. In another example, thecirculation duty cycle may be increased when in cooling mode to improvethe cooling effect caused by air movement, particularly if a higherhumidity is sensed.

Next the method may adjust the circulation duty cycle based on outdoortemperature, as shown at 908. For example, in a heating mode, and if theoutdoor air temperature is high, the HVAC equipment may operate less tomeet heating requirements, so the circulation duty cycle may beincreased to improve air cleaning time that occurs as air is passedthrough a filter. In a cooling mode, the opposite may occur, with thecirculation duty cycle increased if the outdoor temperature is lowcompared to the set point temperature.

The method then may adjust the circulation duty cycle for outdoorhumidity as shown at 910. For example, when outdoor humidity is low andthe system is in a heating mode, the circulation duty cycle (includingventilation) may be decreased to prevent drawing in the dry outdoor air.Alternatively, when the outdoor humidity is high and the system isoperating in a cooling mode, the circulation duty cycle (includingventilation) can be decreased to help prevent drawing in wet outdoorair.

Next, the circulation duty cycle may be adjusted for deviations ofindoor temperature from the set point temperature, as shown at 912. Forexample, when in a heating mode, if the indoor temperature is greaterthan the set point temperature, the circulation duty cycle may beincreased to get more air cleaning time and to eliminate dead/stale airin the indoor space, as well as to de-stratify and equilibratetemperatures throughout the indoor space. Likewise, if in cooling mode,and the indoor air temperature drops below the set point temperature,the circulation duty cycle may be increased to help eliminate dead air,equilibrate the interior space, and improve air cleaning.

Next, the circulation duty cycle may be adjusted based on the programmedschedule period, as shown at 914. For example, a user may be given theoption to increase or decrease ventilation during preprogrammed scheduleperiods, in much the same way that the user may be allowed to adjust theset point temperature based on a schedule. The circulation duty cyclemay be changed, and/or the initial or default circulation duty cyclesmay be different, depending on the schedule period.

Next, the circulation duty cycle may be changed based on occupancy orexpected occupancy, as shown at 916. When the space is unoccupied orexpected to be occupied, the circulation duty cycle may be increased toprovide increased comfort to the occupants. However, if the space isunoccupied, then the circulation duty cycle may be reduced to saveenergy and/or reduce wear on the equipment, particularly since there isno one in the space to notice whether air is circulated or not.

As shown at 918, the circulation duty cycle may then be adjusted basedon time of day. For example, at night the circulation duty cycle may bereduced to avoid making noise while occupants are sleeping. In themorning, when occupants are taking showers and so forth, the circulationduty cycle may be increased to equilibrate humidity throughout thebuilding and to clean the air after an evening of reduced circulation.

The circulation duty cycle may then be adjusted based on the time ofyear, as shown at 920. For example, during spring and fall, thecirculation duty cycle may be increased to accomplish more cleaning ofthe air to remove pollen and other airborne particles that can causeallergic reactions.

Next, the circulation duty cycle may be adjusted based on the sensoroutput of a carbon dioxide, carbon monoxide or other gas or air qualitysensor, as shown at 922. If the air quality sensor(s) indicates poor airquality, such as higher levels of CO₂, the circulation duty cycle(including ventilation) may be increased to bring in fresh air andreduce CO₂ levels.

As shown at 924, the circulation duty cycle may also be adjusted basedon the output of a mold and/or mildew sensor. For example, given aparticular level of sensed mold/mildew and/or spores, the circulationduty cycle (sometimes including ventilation) may be increased toeliminate stale air, clean spores out of the air, and to createequilibration that reduces the likelihood that conditions conducive tomold or mildew growth can occur.

Referring now to FIG. 9B, wherein the circulation duty cycle may beadjusted in response to an airborne particle sensor output, as shown at926. If an airborne particle sensor indicates a higher amount ofairborne particles, additional circulation may be provided to help cleanthe air using the HVAC filter. The above steps are merely illustrativemethods for adjusting a circulation duty cycle, and may be performed inany suitable order. In addition, all of the steps just described neednot be provided. Rather, any combination of the steps may be used,including none of the steps, as desired.

Having determined a circulation duty cycle, the method moves toselecting a random duty cycle adjustment as shown at 930. In theillustrative embodiment, the random duty cycle adjustment is used inconjunction with an HVAC circulation duty cycle that includes two halfcycles per time period, such as per hour. Thus, the circulation dutycycle may include a first “on” time, a first “off” time, a second “on”time and a second “off” time during each hour.

In the illustrative embodiment, the random duty cycle adjustment ischosen to be within a five percent range of the total length of the timeblock used. For example, using a one-hour time block, a five percentrange limit means that the random duty cycle adjustment must be plus orminus three minutes. Any value between negative three and positive threeminutes may be used for the random duty cycle adjustment. Other limitsor ranges may also be used, depending on the application.

The next step includes setting a final circulation duty cycle by addingthe random duty cycle adjustment to the circulation duty cycle asadjusted above, as shown at 930. The final circulation duty cycle isthen converted to a total ON time, as shown at 932, by converting apercentage to an amount of time based on the overall block of time. Todo this, for example, if the final circulation duty cycle is 40%, thenthe total ON time for an hourly cycle would be 40% of sixty minutes, ortwenty-four minutes.

The total OFF time is then calculated as shown at 934. The total OFFtime is simply calculated by subtracting the total ON time from thelength time that is used for the cycle. For example, if the cycle isperforming on an hourly basis, then the total OFF time, in minutes,would be sixty minus the total ON time.

A first ON time is then calculated as shown at 936. First, a random ONtime length adjustment is calculated and used in the setting of thefirst ON time, as shown at 936, by setting the first ON time to be onehalf of the total ON time plus or minus the random ON time lengthadjustment. For example, if a circulation duty cycle is set fortwenty-four minutes in an hour, then two twelve minute cycles may beused. The random ON time length adjustment adjusts both of the twelveminute cycles so that they are unequal. For example, and when using atwenty-four minute circulation duty cycle, and a random ON timeadjustment of two minutes is used, then the circulation time would meetthe twenty four minute goal using a ten minute (twelve minus two) ONtime cycle in combination with a fourteen minute (twelve plus two) ONtime cycle.

A random OFF time adjustment is selected in the same way as the randomON time length adjustment, and used as shown at 938 to set a first OFFtime as being one half of the total OFF time plus or minus the randomOFF time length adjustment. The random OFF time length adjustment isused to modify the OFF times that are used. The second ON time iscalculated as the total ON time minus the first ON time, as shown at940. The second OFF time is calculated as the total OFF time minus thefirst OFF time, as shown at 942.

Next, a random start delay is chosen, as shown at 944. The random startdelay may be used to determine how long the system will wait beforeinitiating the first ON time after the start of a new time period. Thelimits on the random start delay, as noted at 944, are the second offtime and zero. The last OFF time is then calculated as the second OFFtime minus the random start delay, as shown at 946.

The system then runs according to the computed cycle as shown at 948.First, the system waits for the random start delay to expire. Then, thefan is activated for a period equal to the first ON time. The fan isthen shut off and waits for expiration of the first OFF time. Next, thefan is activated for a period equal to the second ON time. Once thesecond ON time has expired, the method shuts off the fan until the lastOFF time has expired, marking the start of a new time period. The methodthen returns to FIG. 9A, as noted at 904, where the circulation dutycycle is readjusted in light of environmental conditions and/or userpreferences.

The methods illustrated herein may be incorporated in whole or in partinto HVAC controllers and systems (such as those illustrated in FIGS. 1and 2A-2C) in any suitable manner. Several embodiments incorporate suchmethods into readable media that is readable by one or more HVACcontrollers and/or which are incorporated into or associated with anHVAC controller.

Those skilled in the art recognize that the present invention may bemanifested in a variety of forms other than the specific embodimentsdescribed and contemplated herein. Accordingly, departures in form anddetail may be made without departing from the scope and spirit of thepresent invention as described in the appended claims.

1. A method of operating an HVAC system of a building, wherein the HVACsystem includes a fan that is operated with fan “on” time periodsseparated by fan “off” time periods to provide a desired circulation inan inside space of the building, the method comprising: generating arandom or pseudo random indicator; and delaying a start of at least oneof the fan “on” time periods by an amount that is related to the randomor pseudo random indicator, while still achieving or substantiallyachieving the desired circulation in the inside space of the building.2. The method of claim 1, further comprising: receiving one or more timedependent parameters; adaptively adjusting the desired circulation levelin the building based in part on one or more of the time dependentparameters; and adjusting one or more of the fan “on” time periodsand/or fan “off” time periods to achieve or substantially achieve thedesired circulation level in the building.
 3. The method of claim 1,further comprising: generating another random or pseudo randomindicator; delaying a subsequent one of the fan “on” time periods of theHVAC system by an amount the is related to the another random or pseudorandom indicator, while still achieving or substantially achieving thedesired circulation in the inside space of the building.
 4. The methodof claim 1, wherein the generating step includes generating a pluralityof random or pseudo random indicators, and wherein different random orpseudo random indicators are used to affect different fan “on” timeperiods, while still achieving or substantially achieving the desiredcirculation in the inside space.
 5. A method of operating an HVAC systemof a building, wherein the HVAC system includes a fan that is operatedwith fan “on” time periods separated by fan “off” time periods toprovide a desired circulation level in the building, the methodcomprising: receiving one or more time dependent parameters; adaptivelyadjusting the desired circulation level in the building based in part onone or more of the time dependent parameters; and adjusting one or moreof the fan “on” time periods and/or fan “off” time periods to achieve orsubstantially achieve the desired circulation level in the building. 6.The method of claim 5, wherein a length of a fan “on” time period isadjusted based on a random number generator, while still achieving orsubstantially achieving the desired circulation level in the building.7. The method of claim 5, wherein a start of a fan “on” time period isadjusted based on a random number generator, while still achieving orsubstantially achieving the desired circulation level in the building.8. The method of claim 5, wherein the one or more time dependentparameters include one or more of: an output from a temperature sensor,an output from a humidity sensor, an output from an air quality sensor,an output from a gas sensor, a time of day parameter, and a time of yearparameter.
 9. The method of claim 5, wherein the desired circulationlevel in the building is also adaptively adjusted based in part on oneor more of: a set point value, a system mode setting, and whether thebuilding is expected to be occupied or unoccupied.
 10. The method ofclaim 5, wherein the receiving, adaptively adjusting and adjusting stepsare performed by a thermostat.
 11. The method of claim 10, wherein thedesired circulation level has a default value stored in a memory of thethermostat.
 12. The method of claim 10, wherein the thermostat has auser interface, and wherein the user interface can be manipulated by auser to change an initial value of the desired circulation level. 13.The method of claim 12, wherein the initial value of the desiredcirculation level is adaptively adjusted by the adaptively adjustingstep.
 14. A method of operating an HVAC system of a building, whereinthe HVAC system includes a fan that is operated with two or more fan“on” time periods separated by fan “off” time periods, the methodcomprising: generating a first random or pseudo random time delay;delaying a start of a first fan “on” time period by an amount that is atleast related to the first random or pseudo random time delay;generating a second random or pseudo random time delay; delaying a startof a second fan “on” time period by an amount that is at least relatedto the second random or pseudo random time delay.
 15. The method ofclaim 14, wherein the first random or pseudo random time delay and thesecond random or pseudo random time delay are different.
 16. The methodof claim 14, wherein the first random or pseudo random time delay is apositive delay.
 17. The method of claim 14, wherein the first random orpseudo random time delay is a negative delay.
 18. The method of claim14, wherein the second random or pseudo random time delay is a positivedelay.
 19. The method of claim 14, wherein the second random or pseudorandom time delay is a negative delay.
 20. The method of claim 14,wherein a length of the first and second fan “on” time periods aredifferent.